1 /*
2  * AC3 parser
3  * Copyright (c) 2003 Fabrice Bellard.
4  * Copyright (c) 2003 Michael Niedermayer.
5  *
6  * This file is part of FFmpeg.
7  *
8  * FFmpeg is free software; you can redistribute it and/or
9  * modify it under the terms of the GNU Lesser General Public
10  * License as published by the Free Software Foundation; either
11  * version 2.1 of the License, or (at your option) any later version.
12  *
13  * FFmpeg is distributed in the hope that it will be useful,
14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
16  * Lesser General Public License for more details.
17  *
18  * You should have received a copy of the GNU Lesser General Public
19  * License along with FFmpeg; if not, write to the Free Software
20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21  */
22 
23 #include "parser.h"
24 #include "ac3_parser.h"
25 #include "aac_ac3_parser.h"
26 #include "bitstream.h"
27 
28 
29 #define AC3_HEADER_SIZE 7
30 
31 
32 static const uint8_t eac3_blocks[4] = {
33     1, 2, 3, 6
34 };
35 
36 /**
37  * Table for center mix levels
38  * reference: Section 5.4.2.4 cmixlev
39  */
40 static const uint8_t center_levels[4] = { 2, 3, 4, 3 };
41 
42 /**
43  * Table for surround mix levels
44  * reference: Section 5.4.2.5 surmixlev
45  */
46 static const uint8_t surround_levels[4] = { 2, 4, 0, 4 };
47 
48 
ff_ac3_parse_header(GetBitContext * gbc,AC3HeaderInfo * hdr)49 int ff_ac3_parse_header(GetBitContext *gbc, AC3HeaderInfo *hdr)
50 {
51     int frame_size_code;
52     int num_blocks;
53 
54     memset(hdr, 0, sizeof(*hdr));
55 
56     hdr->sync_word = get_bits(gbc, 16);
57     if(hdr->sync_word != 0x0B77)
58         return AC3_PARSE_ERROR_SYNC;
59 
60     /* read ahead to bsid to distinguish between AC-3 and E-AC-3 */
61     hdr->bitstream_id = show_bits_long(gbc, 29) & 0x1F;
62     if(hdr->bitstream_id > 16)
63         return AC3_PARSE_ERROR_BSID;
64 
65     if(hdr->bitstream_id <= 10) {
66         /* Normal AC-3 */
67         hdr->crc1 = get_bits(gbc, 16);
68         hdr->sr_code = get_bits(gbc, 2);
69         if(hdr->sr_code == 3)
70             return AC3_PARSE_ERROR_SAMPLE_RATE;
71 
72         frame_size_code = get_bits(gbc, 6);
73         if(frame_size_code > 37)
74             return AC3_PARSE_ERROR_FRAME_SIZE;
75 
76         skip_bits(gbc, 5); // skip bsid, already got it
77 
78         skip_bits(gbc, 3); // skip bitstream mode
79         hdr->channel_mode = get_bits(gbc, 3);
80 
81         /* set default mix levels */
82         hdr->center_mix_level   = 3;  // -4.5dB
83         hdr->surround_mix_level = 4;  // -6.0dB
84 
85         if(hdr->channel_mode == AC3_CHMODE_STEREO) {
86             skip_bits(gbc, 2); // skip dsurmod
87         } else {
88             if((hdr->channel_mode & 1) && hdr->channel_mode != AC3_CHMODE_MONO)
89                 hdr->center_mix_level = center_levels[get_bits(gbc, 2)];
90             if(hdr->channel_mode & 4)
91                 hdr->surround_mix_level = surround_levels[get_bits(gbc, 2)];
92         }
93         hdr->lfe_on = get_bits1(gbc);
94 
95         hdr->sr_shift = FFMAX(hdr->bitstream_id, 8) - 8;
96         hdr->sample_rate = ff_ac3_sample_rate_tab[hdr->sr_code] >> hdr->sr_shift;
97         hdr->bit_rate = (ff_ac3_bitrate_tab[frame_size_code>>1] * 1000) >> hdr->sr_shift;
98         hdr->channels = ff_ac3_channels_tab[hdr->channel_mode] + hdr->lfe_on;
99         hdr->frame_size = ff_ac3_frame_size_tab[frame_size_code][hdr->sr_code] * 2;
100         hdr->frame_type = EAC3_FRAME_TYPE_AC3_CONVERT; //EAC3_FRAME_TYPE_INDEPENDENT;
101     } else {
102         /* Enhanced AC-3 */
103         hdr->crc1 = 0;
104         hdr->frame_type = get_bits(gbc, 2);
105         if(hdr->frame_type == EAC3_FRAME_TYPE_RESERVED)
106             return AC3_PARSE_ERROR_FRAME_TYPE;
107 
108         skip_bits(gbc, 3); // skip substream id
109 
110         hdr->frame_size = (get_bits(gbc, 11) + 1) << 1;
111         if(hdr->frame_size < AC3_HEADER_SIZE)
112             return AC3_PARSE_ERROR_FRAME_SIZE;
113 
114         hdr->sr_code = get_bits(gbc, 2);
115         if (hdr->sr_code == 3) {
116             int sr_code2 = get_bits(gbc, 2);
117             if(sr_code2 == 3)
118                 return AC3_PARSE_ERROR_SAMPLE_RATE;
119             hdr->sample_rate = ff_ac3_sample_rate_tab[sr_code2] / 2;
120             hdr->sr_shift = 1;
121             num_blocks = 6;
122         } else {
123             num_blocks = eac3_blocks[get_bits(gbc, 2)];
124             hdr->sample_rate = ff_ac3_sample_rate_tab[hdr->sr_code];
125             hdr->sr_shift = 0;
126         }
127 
128         hdr->channel_mode = get_bits(gbc, 3);
129         hdr->lfe_on = get_bits1(gbc);
130 
131         hdr->bit_rate = (uint32_t)(8.0 * hdr->frame_size * hdr->sample_rate /
132                         (num_blocks * 256.0));
133         hdr->channels = ff_ac3_channels_tab[hdr->channel_mode] + hdr->lfe_on;
134     }
135 
136     return 0;
137 }
138 
ff_ac3_parse_header_full(GetBitContext * gbc,AC3HeaderInfo * hdr)139 int ff_ac3_parse_header_full(GetBitContext *gbc, AC3HeaderInfo *hdr){
140     int ret, i;
141     ret = ff_ac3_parse_header(gbc, hdr);
142     if(!ret){
143         if(hdr->bitstream_id>10){
144             /* Enhanced AC-3 */
145             skip_bits(gbc, 5); // skip bitstream id
146 
147             /* skip dialog normalization and compression gain */
148             for (i = 0; i < (hdr->channel_mode ? 1 : 2); i++) {
149                 skip_bits(gbc, 5); // skip dialog normalization
150                 if (get_bits1(gbc)) {
151                     skip_bits(gbc, 8); //skip Compression gain word
152                 }
153             }
154             /* dependent stream channel map */
155             if (hdr->frame_type == EAC3_FRAME_TYPE_DEPENDENT && get_bits1(gbc)) {
156                     hdr->channel_map = get_bits(gbc, 16); //custom channel map
157                     return 0;
158             }
159         }
160         //default channel map based on acmod and lfeon
161         hdr->channel_map = ff_eac3_default_chmap[hdr->channel_mode];
162         if(hdr->lfe_on)
163             hdr->channel_map |= AC3_CHMAP_LFE;
164     }
165     return ret;
166 }
167 
ac3_sync(uint64_t state,AACAC3ParseContext * hdr_info,int * need_next_header,int * new_frame_start)168 static int ac3_sync(uint64_t state, AACAC3ParseContext *hdr_info,
169         int *need_next_header, int *new_frame_start)
170 {
171     int err;
172     uint64_t tmp = be2me_64(state);
173     AC3HeaderInfo hdr;
174     GetBitContext gbc;
175 
176     init_get_bits(&gbc, ((uint8_t *)&tmp)+8-AC3_HEADER_SIZE, 54);
177     err = ff_ac3_parse_header(&gbc, &hdr);
178 
179     if(err < 0)
180         return 0;
181 
182     hdr_info->sample_rate = hdr.sample_rate;
183     hdr_info->bit_rate = hdr.bit_rate;
184     hdr_info->channels = hdr.channels;
185     hdr_info->samples = AC3_FRAME_SIZE;
186 
187     *need_next_header = (hdr.frame_type != EAC3_FRAME_TYPE_AC3_CONVERT);
188     *new_frame_start  = (hdr.frame_type != EAC3_FRAME_TYPE_DEPENDENT);
189     return hdr.frame_size;
190 }
191 
ac3_parse_init(AVCodecParserContext * s1)192 static av_cold int ac3_parse_init(AVCodecParserContext *s1)
193 {
194     AACAC3ParseContext *s = s1->priv_data;
195     s->header_size = AC3_HEADER_SIZE;
196     s->sync = ac3_sync;
197     return 0;
198 }
199 
200 
201 AVCodecParser ac3_parser = {
202     { CODEC_ID_AC3 },
203     sizeof(AACAC3ParseContext),
204     ac3_parse_init,
205     ff_aac_ac3_parse,
206     NULL,
207 };
208